1. Field of the Invention
The present invention relates to an integrated circuit for a data transmission system. The invention relates furthermore to a receiving device of a data transmission system.
2. Description of the Background Art
The invention falls within the field of integrated semiconductor circuits (integrated circuit, IC) for data transmission systems, such as, e.g., satellite-based positioning systems (GPS, Galileo, etc.), digital radio and television systems (DRM, DAB, DVB, etc.), mobile communications systems (GSM, UMTS, DECT, WiMax, WLAN, WPAN, etc.), or hard-wired communication systems (Ethernet, ISDN, etc.). It falls particularly within the field of complex integrated circuits, which have a plurality of functional units, such as memory units, interface units, monitoring units, decoders, etc., as well as within the field of the testing of these functional units for their functionality.
Prior-art integrated circuits frequently have a JTAG interface (Joint Test Action Group), standardized according to IEEE 1149, and a so-called TAP controller (test access port) for processing JTAG signals. This makes it possible to check, for example, a microcontroller for its proper operation by running program instructions step by step and interactively (debugging).
To be able to test functional units efficiently for their functionality by the manufacturer of integrated circuits as part of production error tests, prior-art integrated circuits have in addition a test unit, which can be operated in different operating modes. Depending on the operating mode, the test unit connects a plurality of circuit points, each assigned to the operating mode, of the functional units to certain terminals of the integrated circuit. In this way, test signals generated outside the integrated circuit can be applied in a test operating mode directly to circuit points of the functional units, which cannot be influenced externally in the normal operating mode. In addition, signals of the functional units, which cannot be picked up at the terminals of the integrated circuit in the normal operating mode, can be provided at the terminals of the integrated circuit in this way in the test operating mode. Because no additional terminals (pins) on the integrated circuit need to be provided for such error tests, terminals of the integrated circuit, which are also used in the normal operating mode, e.g., for “normal” output signals, are typically used in the test operating mode for the test signals.
It is made possible in this way to efficiently test a plurality of functional units for their functionality, i.e., within a relatively short time period, by placing the test unit successively in different test operating modes; consequently, different signal paths, assigned to the specific mode, within one or more functional units are successively connected to the terminals of the integrated circuit, so that test signals can be supplied at these terminals and the resulting signals can be picked up to test the correctness. The test unit has at least one gate terminal for switching between the operating modes.
It is a disadvantage in this case that for controlled switching of the test unit between operating modes at least one additional separate terminal on the integrated circuit must be provided, which makes the realization of the integrated circuit more time-consuming and thereby more costly. Another disadvantage is that the functionality of the functional units can no longer be tested when the integrated circuit is mounted on a printed circuit board, because the terminals for switching the operating mode are not typically extended to the printed circuit board and therefore cannot be supplied with the appropriate control signals.